text: Since the work by Wilkinson and others on ferrocene a vast amount of work has been done on cyclopentadienyl complexes. It was soon understood by many organometallic chemists that a Cp ligand is isolobal to Tp. As many insights into chemistry can be obtained by the study of a series of closely related compounds (where only one feature is changed) a great deal of organometallic chemistry has been done using Tp (and more recently Tm) as a co-ligand on the metal.
  The Tp, Tm, trithia-9-crown-3 (a sulfur version of a small crown ether) and cyclopentadienyl (Cp) ligands related ligands and form related complexes. These ligands donate the same number of electrons to the metal, and the donor atoms are arranged in a fac manner covering a face of a polyhedron.
  The Tp and Tm ligands are isolobal with the Cp ligands. For example, the Cp manganese tricarbonyl complex is a half sandwich compound, with one face of the Cp ligand binding to the metal atom. The tricarbonyl manganese complex of trithia-9-crown-3 has the three sulfur atoms binding to the metal atom in the same place as the Cp ligand and using the same sort of orbitals for the bonding.
  While the geometry of the Tp ligands do not allow the formation of simple borane complexes with the metals, the geometry of the Tm ligands (and sometimes their bidentate versions Bm) are such that with late transition metals such as osmium and platinum it is possible to turn the Tm ligand inside out to form a borane to which the metal forms a dative bond.
  Here is the manganese complex of Tm with (again three carbonyls).